Bisphenol type aromatic polycarbonate (hereinafter, sometime referred to as "polycarbonate") has been known as a resin for molding which has excellent physical and thermal properties. Such polycarbonate has, however, a high melting viscosity, and hence, molding temperature and molding pressure are higher than other resins, which induces a defect in molding. Further, a molding article of polycarbonate is not only inferior in hardness, but has a defect that it is easy to cause cracking by the concentration of stress in the presence of a certain solvent.
In order to improve these defects of polycarbonate which has a less moldability and less solvent cracking resistance without much damage of an original high impact resistance, transparency and heat resistance of polycarbonate, it has been proposed to incorporate various polyesters into a polycarbonate resin. For example, Japanese Patent Publication No. 37633/1979 discloses to incorporate polyalkylene terephthalate, which is obtained by copolymerization of an ethylene oxide adduct of bisphenol A as a diol component, into polycarbonate. Japanese Patent Laid Open Publication No. 94538/1978 discloses to incorporate polyalkylene terephthalate having a diol component of cyclohexane dimethanol into polycarbonate. Japanese Patent Laid Open Publication No. 145751/1980 discloses to incorporate polyestercarbonate into the composition to improve transparency.
However, the method described in the above Japanese Patent Publication No. 37633/1979 has a disadvantage in industry because it needs an expensive diol such as an ethylene oxide adduct of bisphenol A. The method described in the above Japanese Patent Laid Open Publication No. 94538/1978 brings insufficiently improved solvent cracking resistance because of polyalkylene terephthalate to be incorporated in amorphous polyester. The method described in the above Japanese Patent Laid Open Publication No. 145751/1980 can improve the transparency of a composition of polycarbonate and polyalkylene terephthalate by addition of said polyestercarbonate copolymer. However, when the polyestercarbonate disclosed in the reference is added into a single system of polycarbonate, it is not only difficult to maintain the transparency of polycarbonate itself, but it induces an insufficiently improved solvent cracking resistance.